Errors in adult speech in which misordered consonants and vowels (segmental "Content" elements) obey syllable structure constraints suggest that adult speech has a "Frame/Content" mode of organization, the two components of which may have relatively discrete phylogenetic and neurological substrates. Evidence from preliminary studies of early vocal development and studies by others suggests an ontogenetic succession of "Frames, then Content". It is hypothesized that most variation in vocal activity of early babbling (7-9 months) will involve the vertical, or high-low (Frame) dimension of the vocal tract, as it may be produced primarily by rhythmic sequences of (syllable-like) mandibular elevations and depressions. Consonant-vowel cooccurrence patterns are expected to reflect lack of early flexibility in the horizontal (tongue front-back) dimension. Vertical variation may also reflect a lack of independence between stress and vowel openness. Later developments may increasingly feature intra-episode variation in the horizontal dimension, including more tongue front-to-back variation in successive vowels, more changes in place of articulation in successive consonants, reduction of coarticulation between vowels and consonants, and greater independence between stress and vowel openness. Six subjects will be studied from about 6 months to three years of age using two approaches; 1. Transcription studies, leading to "Macrometric" (large-scale statistical) analyses of infant vocal propensities. Parallel macrometric studies of target language patterns and patterns in other languages will be used to interpret infant vocal propensities; 2. Acoustical studies allowing more objective tests of hypotheses regarding vertical and horizontal variation and its relation to stress. The normative statistical information obtained on infant speech may contribute to more effective diagnosis of speech difficulties in clinical settings.